Chicago Tribune: Sergei Zimov waded through knee-deep snow to reach a frozen lake where so much methane belches out of the melting permafrost that it spews out from the ice like small geysers. In the frigid twilight, the Russian scientist struck a match to make a jet of the greenhouse gas visible. The sudden plume of fire threw him backward. Zimov stood up, brushed the snow off his parka and beamed. “Sometimes a big explosion happens, because the gas comes out like a bomb,” Zimov …